1. Field of the Invention
The present invention relates to an image drum for use in a printing apparatus, and more particularly, to an image drum and a method of manufacturing the same, in which an image drum including a ring conductor can be easily fabricated and a manufacturing cost can be reduced.
2. Description of Related Art
FIG. 1 is a perspective view illustrating a conventional image-forming element according to a conventional art, and FIG. 2 is a partially enlarged cross-sectional view illustrating a portion of the circumferential wall of the image-forming element according to the conventional art. The image-forming element shown in FIGS. 1 and 2 is disclosed in U.S. Pat. No. 6,014,157 by reference.
Referring to FIGS. 1 and 2, a conventional image-forming element 10 includes a hollow cylindrical drum body 12 which is made of metal, preferably aluminum or an aluminum alloy. A plurality of circumferentially extending electrodes 14 are formed on the outer circumferential surface of the drum body 12. These electrodes 14 are electrically insulated from one another and from the drum body 12 and are covered by a thin layer of insulating material. The electrodes 14 may generally be designed depending on the desired resolution of the images to be formed, but are preferably provided densely over the whole length of the drum body 12 to be arranged with a pitch of, for example, about 40 μm in order to realize a resolution of approximately 600 dots per inch (dpi).
An elongate-shaped control unit 16 is mounted inside of the hollow drum body 12 such that a terminal array 18 formed at a longitudinal edge of the control unit 16 adjoins the internal wall of the drum body 12. The control unit 16 is arranged for individually applying a suitably high voltage to each of the electrodes 14 via the terminal array 18 in accordance with the image formation. As shown in FIG. 2, the individual electrodes 14 are formed as grooves separated by adjacent insulating ridges 20 and are filled internally with electrically conductive material 32. Since the electrically conductive material 32 fills in a small diameter hole 24 and a large diameter hole 26 constituting a through-hole 22, the electrodes 14 are electrically connected to zebra-strips 36 disposed at the inner wall surface of the drum body 12 via the through-hole 22. In this case, an anodized surface layer 34 is present at the outer circumferential surface of the drum body 12 and at the internal wall of the through-holes so as to electrically insulate the drum body 12 and the electrodes 14 from each other.
In order to manufacture the image-forming element 10, the cylindrical drum body 12 is provided. The grooves are cut into the outer circumferential surface of the drum body 12, for example by means of a diamond chisel to have a pitch of approximately 40 μm and a width of approximately 20 μm to form the electrodes 14. Alternatively, these grooves may be formed on the outer circumferential surface of the drum body 12 by means of a laser beam or an electron beam.
In the next step, the large diameter holes 26 are cut into the wall of the drum body 12 from inside by, for example, a laser beam. The small diameter holes 24 may also be formed with a laser beam, either from the inside or outside of the drum body 12 to thereby form the through-holes 22. After the through-holes 22 including the small diameter holes 24 and the large diameter holes 26 have been formed, the whole drum body 12 is anodized so as to form the insulating metal oxide layer 34 on the whole surface of the drum body 12. Thereafter, the electrically conductive material 32 fills in the grooves and the through-holes 22. The outer or inner circumferential surface of the drum body 12 is cut to a predetermined depth through polishing so as to effectuate the electrodes 14 and electrical connection portions inside of the through-holes 22. An insulating layer is formed on the outer circumferential surface of the drum body 12 and the control unit 16 is disposed inside of the drum body 12 so as to complete the manufacture of the image-forming element 10.
As described above, in order to form the electrodes 14 on the outer circumferential surface of the drum body 12, the grooves are densely formed over the whole length of the drum body 12 using a precise cutting tool and the through-holes 22 must be formed at regular intervals either from the inside or outside of the drum body 12. Also, after the formation of the anodized surface layer on the outer circumferential surface of the drum body 12 and at the internal wall of the through-holes 22, the electrically conductive material 32 is filled into the grooves and the through-holes 22 and is removed until a desired thickness remains. Specifically, since it is very difficult to evenly form the grooves on the outer circumferential surface of the drum body 12 in such a fashion as to have a pitch of approximately 40 μm and a width of approximately 20 μm and to fabricate the through-holes 22, a manufacturing cost of the image-forming element 10 is significantly high and defect regularly occur. However, the conventional image-forming method and apparatus entails a problem in that a printer made by using such a method and apparatus is expensive, which makes it difficult to sell the printer. As discussed in detail below, there is presently disclosed a direct induction type image-forming method and apparatus using a ring conductor such as the image-forming element described above.